One of the key applications for RFID is inventory control. When an item is tagged with an RFID tag and moved through the supply chain, the ability to track the RFID tag facilitates the operation of the supply chain. However, RFID readers are not installed to cover the whole supply chain due to the cost and complication with such an approach. Instead, RFID readers are deployed at the check/transition points along the supply chain, e.g., at a loading dock door between the warehouse and truck, at a doorway between backroom and retail floor, etc. RFID readers in these locations are sometimes referred to as portal readers. The RFID tags on the items are supposed to be read only when the item passes through the portal. However, some “long range” RFID tags are generally designed to maximize the gain and efficiency of their antennas. This mixed tag environment results in long range RFID tags that are near the portal but beyond the doorway being unintentionally read, leading to errant tracking of the tagged item. This problem is generally referred to as over-range problem.
To limit the range of the RFID reader to the doorway, a reduction of the reader transmit power is sometimes used. This approach requires that all RFID tags have a similar read range. As other RFID applications have developed, some items now require the use of a small “short range” tag which has a lower read range. The small tag is not able to be read with the reduced transmitted power. Therefore, configuring the transmit power of the RFID reader to accommodate all tags in this mixed tag environment results in either over range or a failed read.
In addition to reducing the level of transmit power as described above, others have attempted to improve the performance of the small tag. Due to the physics behind the electromagnetic radiation and the interaction of antenna configuration of the RFID tag, such attempts inefficiently result in a physically larger tag than is actually required for the application.
RFID readers having more complex antenna systems have been designed to focus the RF field and restrict read range to a limited area or volume. However, the deployment of complex antenna naturally results in higher cost.
Therefore, what is needed is a system and method to discriminate between short range RFID tags and long range RFID tags and only read tags passing through an RFID interrogation zone, e.g., RFID portal.